League of Legends had a ban mechanic in ranked play that includes an odd little quirk. Each team gets 3 bans which their captain chooses in a round-robin style. In solo/duo queue, the team captain is the person with the highest hidden ELO. At my relatively low level, the Bans are frighteningly predictable. In nearly every game, the following champions are banned: Malphite, Blitzcrank, Amumu and Shen. There is a second tier of bans that includes Darius, Elise, Nidalee and Hecarim.
Pick 3-4 of the first group, mix with 1-2 of the second group and occasionally throw another random champion in there and you have your bans. I'm not sure I've played a game that hasn't had three of the first four list banned.
What makes these champions so frequently and consistently banned? Each of them offers game changing abilities. They aren't overpowered in the "ZOMG we have to nerf them for the sake of the game!!!" sense. But they have abilities that, if used correctly, can catch a winning team completely off guard and flip a game on its head.
Malphite has, arguably, the best initiate in the game. Knock-ups aren't affected by tenacity or cleanse and it's a large AoE with a large range. He builds very tanky so being in the middle of the enemy is fine. Throw on top of that a PBAoE attack speed debuff and you have a nasty little package.
Shen is an energy based champ allowing for early harass and sustain (through his shield). He also tends to build tanky and can split push like a fiend. His ultimate gives him both an escape, an emergency shield and a teleport all in one neat little package with a relatively short cooldown.
Amumu has a great initiate and a huge AoE ultimate with a very powerful side affect (rooting and prohibiting auto-attacks). Additionally, he does % health damage, builds tanky and jungles very well.
Blitzcrank is the swingiest champion in the game. It often only takes one late game pull to swing a game. Throw on top of that a somewhat spammable AoE silence and a knockup and you have a champion that is very difficult to play against.
Are there really better choices?
If you're first pick, why not force the other team's bans? Here's my suggestion to team captains who are picking first: ban other people. Ask your mid lane who he doesn't want to play against and find out if anyone is particularly annoyed by certain champions. Make sure that someone on the team can play the Power 4 (usually they can). If your mid lane wants to play Diana, spending two picks to take out Kassadin and Mordekaiser might not be a bad idea. Removing other global ultimate champions such as Twisted Fate or Nocturne can also work really well.
Personally, I've started banning Kassadin, Shaco and then one ban targeted to who it looks like we're going to get (Cho'Gath vs Malphite, Jayce vs Shen, Alistar vs Blitzcrank or Kha'Zix vs. Amumu). Kassadin's ability to roam is fairly powerful and a halfway decent Shaco will create problems mid lane most of the time. Then I'll first pick the champ that's left. Generally, I'll switch to someone who called that position but all of those champions are ones I'm comfortable with for exactly this reason.
As a reference, the current most popular champions are: Taric, Caitlynn, Lux, Miss Fortune, Xin Zhao, Ezreal, Jarvan IV, Leona, Lee Sin, Tristana.
I've italicized the ones that I'd recommend to banning if you don't have another strategy.
Taric is still a very powerful champion that people are starting to play in other positions. Riot just released a patch that further nerfs him so this may not remain but it wouldn't surprise me if we continue to see him frequently.
Lux has a stupidly long range poke and zoning ability with her combo. Her laser does lots of damage to multiple targets and can get a cooldown as low as 24 seconds. She clears minion waves very well and her shield gets to be HUGE late game when she can stack AP. At higher skill levels, this is not a necessary ban but at lower skill levels, she represents a relatively big swing because she's fairly easy to play and requires good game knowledge to play against.
Miss Fortune has the highest win rate ADC in League right now at nearly 60%. Picking her or banning her seems like the right thing to do.
Xin Zhao is still a very strong jungler. Yes, he got nerfed. But his nerf simply stopped him from perma slowing and trimmed his ultimate damage slightly. It didn't actually diminish much of his kit's core power. He's still being picked a lot and he's still winning a lot.
Jarvan IV just got the nerf bat so this one may not be necessary. He was probably the strongest jungler leading up to this week but the loss of his armor aura for his standard may be too big a hit to take. He's certainly no longer a slam dunk first pick for most teams.